Railroad grade crossings have always posed a danger to vehicles using them. The size and momentum of a train as compared to vehicles which use the crossing, i.e. automobiles, buses and trucks, is so great that a direct collision between a train and a vehicle at a crossing such as an automobile or truck results in not only the total destruction of that vehicle but the death or serious injury of the occupants of the vehicle. The speed and momentum of a train approaching a grade crossing is such that there is little if any chance for the train to stop before reaching the crossing once the engineer of the train knows such a collision is imminent.
Building a viaduct over or under the rail line is generally prohibitive given the cost of construction and subsequent maintenance necessary to maintain it. Thus, the general methods of preventing accidents at a railroad grade crossing rely on providing systems which warn vehicles which use the crossing of the impending approach of a train and lower barriers or gates into place to restrict access to the crossing in the critical seconds before the train arrives at the crossing.
Two systems in wide use today are a standard track circuitry and vital relay network. Most rail lines are sectioned into large long blocks for control and monitoring purposes. The standard track circuitry is a common type of train presence detection circuitry used to detect the presence of a train within a block of track. The vital relay network is a series of relays used to control railroad crossing warning lights and the raising and lowering of primary protective crossing gates. The protective crossing gates generally being gates on the entrance lanes into a crossing. Both of these systems work in conjunction with each other and detect trains by means of electrical conductors across the rails as current flows through rail car wheels. A protected crossing located in the block, ideally at its center, has a vital relay network. Upon receipt of a signal from the standard track circuitry, that a train has entered the block and is approaching the crossing, the vital relay network activates the crossing warning lights and then lowers the crossing gates.
A two gate arrangement as depicted in FIG. 2A is a very common arrangement used to restrict access to a railroad crossing. However, the open exit lanes in the two gate arrangement present their own serious problems in that they allow impatient drivers access to the crossing even though the entrance lanes have barriers across them. Such easy circumvention of the safety barriers of a two gate crossing creates significant dangers in any situation and especially on a rail line that has frequent high speed trains using the line every day.
An alternative to the two gate system is the four gate arrangement as depicted in FIG. 2 which has two additional gates at the exit lanes to the crossing. However, the four gate systems have their own problems. For instance one common problem is the entrapment of a vehicle within the protected area of a four gate crossing because the gates are lowered prior to the vehicle being able to exit from the protected area of the crossing as a train is approaching. Once these vehicles become entrapped between the gates, there is little opportunity for them to escape and avoid being hit by an on coming train. A number of systems currently exist which attempt to deal with the problem of vehicle entrapment; however, these systems are expensive and difficult to install and maintain. A number of them rely on large loops which must be buried in the ground fairly close to the surface of the ground. Additionally, many of these systems lack the capability to respond to wide variety of conditions and circumstances.
Thus, what is need is an inexpensive and easy to install and maintain method and system which allows a vehicle to escape from a four gate protected crossing while retaining all of the advantages of the four gate grade crossing. A system that can also respond to and deal with a wide variety of different conditions and circumstances.